Protective plating for electrodes



by L.i'1.r%5%- Q6. M

' ATTORNEY L. A. WOOTEN PROTECTIVE PLATING FOR ELECTRODES Flled Jan 91947 Dec. 26, 1950 Patented Dec. 26, 1950 PROTECTIVE PLATING FORELECTRODES Leland A. Wooten, Summit, N. J assignor to Bell TelephoneLaboratories,

Incorporated, New

York, N. Y., a corporation of New York Application January 9, 1947,Serial No. 721,139

4 Claims.

This invention relates to discharge devices and is specifically directedto protection for electrodes of such devices in which said electrodesare subject to bombardment by electrified particles which may in turncause disintegration of the bombarded surfaces of said electrodes.

Such electrodes as are subject to said bombardment are normally requiredto dissipate by radiation or by conduction or by both the heat generatedby such bombardment and, of course, heat produced therein by other meansduring normal operation of such a device. Said electrodes are requiredalso to be conductive electrically since some are employed as actualelectrical circuit paths for electron flow while others are employedprimarily as structures responsive to nearby acceleration of electrifiedparticles but are nevertheless subject to unintentional collisiontherewith and collection thereon of some of said particles, disposal ofwhich particles is necessary to prevent accumulation of undesirablespace charges or electrostatic charges on such structures. A typicalexamples of the latter is the well-known magnetron cavity type anode.

In order to combine good electrical and thermal conductivity withrefractory properties, and since these two groups of characteristics donot exist in practical ratio in any one known material, prior art hasfound it advisable and necessary to emolcy as electrode ma erial s chmaterias as iron and copper and the noble. metals and various well-knownalloys of these types. These materials have practical values of thermaland electrical conductivity for the various use made of same. It is wellknown that such materials as indicated and others of like character anduse not specifically mentioned do not possess the required refractoryproperties to withstand bombardment without attendant injuriousdisintegration.

. This deficiency has been recognized heretofore and the problem hasbeen met in a number of ways in a number of special instances. For

the condition wherein the electrode is not required to dissipate a largequantity of heat, pure refractory metals such as silicon, tungsten,molybdenum, etc., or alloys thereof have been used as the basicelectrode material. However, in cases where such electrodes have beenrequired to have a rather high thermal conductivity, refractorymaterials obviously could not be used as the basic electrode material.Nevertheless, such materials having properties similar to those 'ofmolybdenum or tungsten have been finely 2 powdered and applied toelectrodes made of less refractory material such as iron, copper, etc.,by means of a binder of, for instance, pure silica.

Somewhat similar to the latter arrangement and also heretofore known isthe use of a sheet or ribbon of pure molybdenum, or material of similarrefractory characteristics, as a lining or covering for electrodesurfaces such as those of a magnetron anode which is subject tobombardment. Such linings or coverings have been held to the protectedelectrode by mechanical means such as press fits or resilience of thelining or coating or by means of special configuration of the surface tobe lined or covered which held the material in place. The art is lackingin respect to disclosing the application of plated layers of such purerefractory materials as molybdenum, tungsten, or the like to electrodebodies of high electrical and thermal conductivity. A device enclosingelectrodes so treated will have the obvious advantages of both anelectrode body of high thermal and electrical conductivity and also ofrefractory surface character to inhibit disintegration thereof byelectron bombardment and a strongly adherent condition between the bodyand the surface material. The prior art does not teach such an adherentrelationship between such bodies and previously mentioned types ofsurface layers for same.

It is the object of this invention to provide electrodes whose bodymaterial is of low refractory nature and of high electrical and thermalconductivity, with a strongly adherent plated surface layer thereon ofmetal having characteristics similar to those of molybdenum or tungsten.This latter type of metallic material is recognized as having goodrefractory characteristics capable of inhibiting disintegration ofelectrode surfaces which are covered therewith and which are bombardedby electrified particles.

As an exemplary disclosure, the invention may be explained in connectionwith a magnetron anode of the multicavity type employed in highfrequency generation. The anode is in the form of a toroid havingequally spaced cavities formed in the inner wall of said toroid andcompletely through the thickness of same. Each cavity has an openinginto the inner space of the toroid. Between the said opening of adjacentcavities are portions of the inner surface of the toroid. It is uponthese latter portions that the plating of molybdenum or tungsten or thelike is used. The energized filament of the magnetron is axially locatedwithin the inner space of the toroid such that by location of a suitablemagnetic field acting substantially parallel to said filament a is wellknown, said filament emits electrons which accelerate in spirals pastthe said cavity spaces to excite said cavities for generation therein ofhigh frequency electrical energy.

The electrons so accelerated by the anode voltage and the axial magneticfield have occasion to impinge upon the exposed inner toroid surfaceportions which separate respective cavity openings. It has been found,and is well known, that the body of the magnetron, usually made ofcopper, will disintegrate injuriously under such bombardment unless thesaid magnetron is properly aged. The expression aged is well known inthe art to designate a process whereby magnetrons and other dischargedevices of like character and function are specially processed prior touse to enable same to withstand rigorous operating conditions such asheavy loads of current or excessive heat or bombardment of surfaces byelectrified particles, among various other such conditions.

If the bombarded anode surface of such a magnetron is plated with a thinstrongly adherent layer of, for instance, molybdenum, the aforementionedaging process is not necessary to prevent disintegrat on of the anodesurfaces, which usually results in operation at the wrong ,frequency, ifat all, and with loss in power extractable therefrom.

V The manner of obtaining this thin strongly adherent plating ofmolybdenum or like material is in brief depositing same on the surfaceto be plated by decomposition of a gaseous carbonyl of the platingmaterial at the said surface. One apparatus and procedure which may beused to so plate magnetron anodes in accordance with the invention isdisclosed in a copending jont application of L. H. Germer and G. E.Reitter, Serial No. 653,868, filed March 12, 1946. Any disclosure ofthis aforementioned application dealing with production of a magnetronanode plated with a layer of molybdenum, tungsten, or the like is anexemplary disclosure of the present invention and the Germer-Reitterdisclosure of such production referred to is considered as incorporatedin this disclosure as if fully included herein.

Folowing is a detailed description of the invention and is set forth inconnection with the attached drawings of which the following are generaldescriptions.

anode block of Fig. 2. subsequent to machining of same;

Fig. l shows a completed anode in perspective and subjected to amagnetic field; and

7 Fig. is a plan view of such a magnetron anode as is shown in 4 anddiagrammatically indicates electrical connections thereto to illustratesubsequent detailed description concerning the uti'ityof the invention.

In Fig. 2 is illustrated a toroidal block I of copper having its innersurface 2 plated with a thin layer of pure refractory metal such asmolybdenum. Molybdenum is indicated as a specific material suitable forthis application but the invention is intended to cover other suchmetallic plating materials having refractory character'stics similar tothose of molybdenum or tungsten as reated to their ability to inhibitdisintegration thereof by bombardment of same by electrified particlesand their ability as thin layers not to detract substantially from theelectrical and thermal conductivity properties of the body upon whichthey are plated.

In Fig. 3, the block I of Fig. 2 has been machined to produce therein aneven plurality, namely, twelve, of equally spaced cavities such as 3extending the. full thickness of the block I. Fig. 5 shows more clearlythe angular relationship between these cavities 3. Slots 4 are machinedin the walls separating the cavities from the inner space of thetoroidal block. It is well known that the size of the block I, of thecavities 3 and of any other holes, slots, ridges, etc. associated withthese cavities will affect the irequency of the energygenerated from amagnetron containing this well-known type of anode structure and thatconsequently the machining operations referred to herein should beprecise in accordance with well established practices in the art.

As illustrated best in Fig. ,1 a circumferential slot 5 is .machined inboth ends of the block :I and in the bottom of this slot 5 are machinedtwo additional narrower slots 5 and 1 radially separated irom eachother. The sequence of machining slots 4 through J is not fixed butpreferably is in the order of sots 5, 6 and 'I' and then slots 4. Thisorder lends to facility of machining but is not mandatory. Into theseslots 6 and 1 are inserted respective r ngs 8 and 9, preferably made ofsilver. Ring 8 for instance is used to interconnect or strap alternatecavities by having' lugs thereon attached to the connecting wall betweenadjacent cavities at every other cavity. Ring 9 is used to interconnector strap the remaining group of alternate cavities by means of. similarlugs, one of which is designated It) in Fig. 1. Such strapping ofalternate cavities in general is well known to stabiize the operation ofsuch ma netron anodes and the specific manner of so doing which is shownhere is'fully disclosed in the copending application of J. B. Fisk,Serial No. 529,619, filed April 5, I944.

Fig. 4 as briefly described prev ously, shows a comp eted magnetronanodeembodying the invention. All through the previous machining andfittin operations the thinly plated layer' 2 of molybdenum has beenretained on whatever remained of the inner surface of the orig naltoroidal block I of Fig. 2'. In Fig. the silver rings 8 and 9 are shownassembled or fitted into their respective narrow slots 6 and 1 in thelarger circumferential slot 5 as more clearly shown in section in Fig.l. The arrows I! are intended to illustrate that a magnetic field I"! isto be applied to the magnetron anode area in substantially an axialdirection thereto as is well known in operation of such a device.

With reference to Fig. 5, a plan view of such a ma netron anode as shownin Fig. 4, the body I of the anode is grounded at l3, the filament II isconnected to a negative potential I2, the magnetic field I! issubstantially perpendicular to and into the drawing and an output loop[4 is attached to one of the cavit'es 3. All of these features of Fig. 5are conventional. I have illustrated the path IE or" an electron whichis permitted to bombard the anode surface '2 at area l6 within theevacuated inner anode space. The manner in which such a magnetronfunctions to permit high frequency energy to be withddrawn by means ofloop I 4 is sufficiently well known that description of such operationis unnecessary for the purpose of explaining the present invention.

If the surface 2 of the anode block I were not coated with a thinplating of, for instance, molybdenum or other similar metal inaccordance with the invention and if the magnetron diagrammaticallyrepresented in Fig. 5 were not aged, then repeated bombardment of theanode surface 2 would cause disintegration of the copper which in itselfis a poor refractory material. Copper is chosen for such magnetronanodes because of its ability to conduct heat and electricity rapidly. Apurpose of the invention is to protect this desirable body material witha thin layer of highly refractory material which will adhere strongly tothe copper body and. prevent deterioration of the surface 2 bybombardment while at the same time not affecting appreciably thesubstantial thermal or electrical conductive properties of the main bodyof copper. It is, of course, intended that the disclosure of copper inthis exemplary embod'ment of the invention does not preclude within thescope of the invention the use of other anode or electrode body materias such, for instance, as iron or silver or alloys of any of these singlyor in combination.

Such layers of refractory material as the pr or art teaches, such aspowdered metal bonded with silica or pure refractory metals in the formof ribbons or strips mechanically fixed to said body members, are notconsidered as stron ly adher nt in that they may be removed entirely orin part by vibration and shock or other conditons and cannot representas close a mechanical, electrical and thermal union as a plated ayer. Inaddition. a plated aver, and probably equally well a ribbon or strip aspreviously mentioned, presents a more complete and effective refractorybarrier or protector for the body material. A plated layer performs a lthe functions of the pr or art coatings or layers and in ad itionprovides a reliab y strong adherent condition not found in the art.

An a paratus exemplary of the t pe suited to production of this platinof mol bdenum or tun sten on such a ma netron anode as is disclosedherein is fully disclosed in the aforementioned conendnq appication ofGerm r and Reitter. This apparatus employs the princi le ofdecomposition of a metallic carbonyl at the surface, such as 2 on thedrawing. to be p ated. The application of such a plating to the surfaceof an electrode subject to bombardment, such as the magnetron anodedisclosed herein,. prior to machin ng of such a structure if same isrequired, results in an article of manufacture or of structure notheretofore known.

In the Germer-Reitter application is disclosed a supply reservoir in theform of an elongated closed tube which may be loaded with a large numberof articles, this reservoir be ng then attached to the plating chamberby gas-tight means; a closed gas-tight receptacle is provided and alsoattached to the plating chamber by gas-tight means; the entire apparatusis then evacuated; the articles to be p ated are fed one by one througha heating element heated to a desired temperature, then fed into a zoneto wh'ch the plating gas is supplied to them while they are maintainedin a heated condition and after being plated upon the desired surfacethey are ejected into the receptacle. After the entire number is finshed the plated articles may be emptied from'the receptacle and a newsupply placed in the supply reservoir and the operation repeated. i

' In plating magnetron anodes by the above type of apparatus inaccordance with the present invention, the object is to plate theinternal surface of the toroidal-shaped blocks to a maximum extent withlittle or no plating upon other surfaces. This object is accomplished bythe invention of Germer and Reitter. Exposing the desired surface orsurfaces to a carbonyl of the particular refractory metal to be used asthe plated layer and carefully contro ling and regulating temperaturesbefore and during the exposure will produce a strongly adherent platingin accordance with the present invention. A more detai ed disclosure ofthe above briefly described apparatus for prod cing structure accordingto the present invention will be found in the above-referencedapplication of Germer and Reitter.

It is, of course, obvious that the plating arrangement disclosed hereinwith reference to a magnetron anode may be ap lied by modification threof to other types of electro e structures such as anodes of glass ormetal enclos d vacuum tubes from which anodes considerable heatdisspation is required and which are subject to in urious bombardment ofelectrified partic es, electrons or otherwise. It is not intended thatthe scone of the invention sha l be limited to the s eci c t pe of anodeused as the exem lary disclosure since it is apparent that the inventioncontemplafis e' uivalent structures w erein use of the invention is forthe purposes d sclosed and claimed herein, Furthermore, the in ent onmay be used in connect o with anod s which are not necessarly reouiredto dissi ate large amounts of th rmal ener y. In the latter case thethinness of the plat d la er becom s of prime importance so as not todetract too effectively from the conducti e p o ert es of such eectrodes. The thickness o thinness of such plated layers are controllale b mea s of the apparatus and procedur d s los d by Germer andReitter, supra.

What is c aimed is:

1. A magn tron anode of t e multicavity type having a copp r body, aworking s rface of said body ha ing ther on a th n strongly adh rentplat d layer of a metal selected from the group consisting of molybdenumand tungsten.

2. A magnet on anode of t e mult cavity type having a toroidal copperbody the inner working surfaces of the said toroi al body ha ing thereona thin stron ly adherent plated layer of a metal se ected from the groupconsisting of molybdenum and tun st n.

3. The process of making a magnetron anode of the multicayity typeconsisting of producing a solid toroidal block of copper, plating theinner surface thereof with a thin strongly ad erent layer of a metalselected from the group consisting of molybdenum and tungsten andsubsequently machining said block to form cavities therein spaced fromeach other circumferentially of said block and to form openings fromsaid cavities to the inner space of said block.

4. A magnetron anode of the multicavity type having a toroidal copperbody, said body having flat end surfaces and having cavities thereinalmost totally enclosed laterally by said body and meter of. said body,said body also having slots:

therein, each slot extending between said end surfaces and between. adifferent cavity and. the inner space at said toroidal body, the Workingsun-- faces of said anode body bounding the periphery of said innerspace and separated from each other by said slots having thereon a thinstrongly adherent plated layer of metallic molybdenum.

LELAND A.= WOOTEN.

REFERENGES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,872,359 Sutherlin Aug. 16, 1932 7 2,019,634 Rentschler Nov. 5; 1935 2,149,658 Armstrong Mar. 7,1-939 2,347,501- Penker Apr. 25, 1944 2,388,737 Gotha Nov. 13; 19452,424,576 Mason July 29, 1947

